1. Field of the Invention
The present invention relates to a vibration generator in which a weight body is vibrated by a driving force applied to the weight body from a magnetically-driven portion composed of a coil and a magnet, and more specifically, to a vibration generator in which resonance points of vibration are set to two frequencies.
2. Description of the Related Art
Various electronic devices such as a controller of a mobile phone or game machine and the like are provided with a vibration generator. The vibration generator has a weight body that is supported by a spring in a small case. One of a coil and a magnet, composing a magnetically-driven portion, is supported by the weight body, and the other is provided in the case side. When an alternating current is applied to the coil, a vibration driving force is applied to the weight body from the magnetically-driven portion such that the weight body is vibrated.
In this type of vibration generator, the frequency of the alternating current applied to the coil of the magnetically-driven portion is caused to coincide with a natural frequency determined by the mass of the weight body and the elastic modulus of the spring. Then, the weight body can resonate, thereby obtaining large amplitude of vibration.
In the conventional vibration generator, a resonance frequency is set to one point. Therefore, when the frequency of an alternating signal applied to the coil greatly deviates from the natural frequency, the vibration amplitude of the weight body during vibration cannot be increased. Further, when the resonance frequency is set to one point, the vibration generator can only generate one kind of vibration, and cannot generate two kinds of vibrations having vibration frequencies that are different from each other.